Process of producing a permeable synthetic film

ABSTRACT

A poromeric film is provided which is based on a polymer cement of polyurethane, polyvinyl chloride, and plasticizer. No internal non-solvent is used. The cement is applied to a water permeable substrate and coagulated in a water bath.

United States Patent [19] Murphy Oct. 16, 1973 PROCESS OF PRODUCING APERMEABLE SYNTHETIC FILM [21] App1.No.: 194,526

[52] US. Cl 117/63, 117/l35.5, 117/161 KP [51] Int. Cl B44d l/44 [58]Field of Search 117/161 KP,63,, 135.5;

[56] References Cited UNITED STATES PATENTS 3,514,307 5/1970 Hallenbeckll7/8 8/1963 Holden 117/161 KP 1/1959 Schollenberger 117/161 KP UXPrimary Examiner-William D. Martin Assistant Examiner-Theodore G, DavisAttorneyA1bert C. Doxsey et a1.

1 5 ABSTRACT A poromeric film is provided which is based on a polymercement of polyurethane, polyvinyl chloride, and plasticizer. No internalnon-solvent is used. The cement is applied to a water permeablesubstrate and coagulated in a water bath.

2 Claims, No Drawings PROCESS OF PRODUCING A PERMEABLE SYNTHETIC FILMBACKGROUND OF THE INVENTION The manufacture of poromeric permeablesynthetic films suitable for shoe uppers by dissolving prepolymerpolyurethanes in a solvent such as dimethyl formamide, spreading thecement on a substrate and coagulating by exposure to moist air, water ora mixture of water and polymer solvent is known. Generally internalwater is required in the polymer cement to form colloidal dispersions ornear colloidal dispersions. This feature in turn requires thatcoagulation baths of mixed solvent and water be used for best results.Process control in a plant is difficult.

The manufacture of poromeric films by dissolving essentially linearpolyesterurethanes in dimethyl formamide in the presence of athixotropic viscosity improver and sufficient internal water to producea cement cloud point of 40 95C is also known. The cement is spread on'asubstrate, given an air set of several minutes to precipitate polymerand washed in water to remove residual solvent. The elevatedtemperatures used in this process can lead to solvent loss anddegradation of cement viscosity. Control of plant process conditions isdifficult.

Other synthetic materials in the form of films are used for lower costshoe uppers. Chief among these ma- I terials is polyvinyl chloride filmwhich is formed as in a calendering or in a casting process.Polyvinylchloride film is inexpensive compared to polyurethane film andforms attractive shoe uppers. A polyvinyl chloride shoe upperof thistype is, however, impermeable to air and water vapor. It is notporomeric in nature and shoes made with this type of upper areintolerably uncomfortable to many people, particularly when'worn for aperiod of more than a few hours in succession.

Polyvinyl chloride materials have been made breatheable by punchingholes in them, which leaves an unattractive film. Other efforts to makebreatheable polyvinyl chloride films include adding fillers such assalt, walnut shells, water soluble powders and noncompatible liquidssuch as ethylene glycol to the cement, spreading the films, then washingthe noncompatible component out with water or other elutant which isnon-solvent for polyvinyl chloride. These processes are not widelypractical because of huge quantities of water that are used andcontaminated and the difficulty in obtaining complete removal of thenoncompatible material.

The present invention is a specific combination of specific ingredients,all known in the prior art, but not heretofore taught in the specificcombination shown herein. Even with this invention it has not beenpossible to make practical poromeric films based on polyvinyl chlorideas the sole polymer, but it has become possible to make practicalporomeric films wherein an essentially linear polyurethane containingsubstantially no free hydroxyl or isocyanate end groups is combined in aminor amount, based on weight of polymer plus plasticizer, with a majoramount of combined polyvinyl chloride and plasticizer for such polyvinylchloride. The prior art has taught that prepolymer polyurethanes chainextended with a compound having two active hydrogen atoms bounded toamino-nitrogenatoms can be combined with polyvinyl chloride to formcements for producing poromeric film, but has found that it ispreferable to keep the proportion of polyvinyl chloride at 50% orless'by weight of total polymer present whether or not any plasticizerwas combined with the polyvinyl chloride. In US. Pat. No. 3,100,721 suchmixtures are shown, but to produce a satisfactory poromeric material,polyvinyl-chloride is combined with the polyurethane in levels of 25 50percent by weight. Further, the use of plasticizers with the polyvinylchloride component is discouraged. The polymer mixture is dissolved in asolvent such as dimethyl formamide and enough of the non-solvent for thepolymer, such as water (internal water) is added to form a colloidaldispersion before spreading the film upon a substrate.

United States Pat. No. 3,208,875 describes the preparation of poromericfilms from polymer cements preferably containing in the cement an amountof fluid.(internal water) which is a non-solvent for the polymer, saidamount being up to, but less than, the amount required to bring aboutformation of a colloidal dispersion. This process further requires thatthe polymer film be coagulated in a bath of mixed solvent nonsolvent forthe polymer with the solvent content of the bath preferably above 50percent. The presence of internal water is to help against the formationof macrovoids in the coating and to speed the coagulation process. Inpracticing these teachings it has been observed that when dimethylformamide polymer cement, containing as the polymeric portion either allpolyvinyl chloride or polyvinyl chloride containing up to 50 partsplasticizer, is employed to produce a film-forming layer on a substrateand the polymer is coagulated in a bath of either pure water or mixedwater solvent, the resulting film is somewhat poromeric in nature, but,is too stiff and brittle at low levels of plasticizer, and when highlyplasticized is too low in moisture vapor transmission to be adequate asa useful poromeric film. Poromeric films of the prior art depend greatlyfor their success upon the presence in the polymer cement of at least 50percent by weight polyurethane when polyvinyl-chloride is present.

The present invention enables one to prepare poromeric films of mixedessentially linear polyesterurethane and polyvinyl chloride and raisethe proportion of lower cost polyvinyl chloride plus plasticizertherefore to as high as percent by weight based on polymer plusplasticizer present, permitting substantial cost reductions from thecost of polyesterurethane poromeric films. The compositions of thepresent invention have further advantages over compositions of the priorart. The major elements present are a particular polyvinylchloride, aparticular essentially linear polyurethane, a particular plasticizer anda particular solvent. No internal water is needed to create colloidalsolutions or dispersions of coating cements. No high temperature cloudpoint cements are needed, and no thixotropic thickening viscosityimprovers are needed. The cements are made and spread at roomtemperature for wet thicknesses to about 60 mils. For wet thicknessabove 60 mils cements are spread at 50 C. No air set time is speciallyrequired to coagulate polymer but provision of an air set period hasbeen found to give product with somewhat better cell structure andbetter absorptivity of toner dye when in the form of a poromeric film.The cement can be run directly to a bath containing water only. Nosolvent is required in combination with water in the bath. Theextraction bath can be hot water up to 45 to 75 C for rapid extractionof solvent.

SUMMARY OF THE INVENTION The art has broadly shown combinations ofpolyvinyl chloride and polyurethane polymers for use in formingporomeric films. The use of plasticizers with polyvinyl chloride isknown. For a leatherlike film to be successful as a commerciallyacceptable poromeric material, it must have a moisture vaportransmission(MVT) of at least 650 g/sq.m./24 hours. The test procedure of theFederal Specifications on Leather Methods of Sampling and Testing,KK-L-311A, method 8011 is followed to determine MVT. Further, the filmmust be able to perform at least 100,000 flexes on the Bally Flexometerat 35F.

The particular polyvinyl chloride resin found useful in this inventionis a high molecular weight homopolymer. Low molecular weighthomopolymers and copolymers have been tried and found to giveunsatisfactory permeable film formation when coagulated in water fromdimethyl formamide cements. A polyvinyl chloride resin, inherentviscosity 0.95, specific viscosity 0.44, specific gravity 1.4, particlesize percent less than 75 130 microns, 90 percent less than 130 200microns is preferred. Such resins are available on the market. They arefree flowing powders of granules readily soluble in the hygroscopicsolvent dimethyl formamide. Larger particle size ranges than thoselisted above are acceptable as long as the resin dissolves readily indimethyl formamide. The cement recipes of this invention are based on100 weight parts of polyvinyl chloride.

The particular essentially linear polyurethanesuseful in this inventionare essentially linear polyesterurethanes prepared by the processes ofUS. Pat. No. 2,871,218. These materials are characterized by beingthermoplastic, extrudable to a film and substantially free ofcross-links. They are soluble in dimethyl formamide and also may beformed into a film of desired thickness by spreading as a cement andevaporating the solvent. The polyesterurethane elastomers are preparedby heating a mixture comprising (1) one mol of an essentially linearhydroxyl terminated polyester of a saturated aliphatic glycol havingfrom-4 to 10 carbon atoms and having hydroxyl groups on its terminalcarbon atoms, and a material selected from the group consisting of adicarboxylic acid of the formula I-IOOC-R-COOH where R is an alkyleneradical containing from two to eight carbon atoms and its anhydride,said polyester having an average molecular weight between 600 and 1200and having an acid number less than 10, and (2) from about 1.1 to 3.1mols of a diphenyl diisocyanate having an isocyanate group on eachphenyl nucleus in the presence of (3) from about 0.1 to 2.1 mols of asaturated aliphatic free glycol containing from 4 to 10 carbon atoms andhaving hydroxyl groups on its terminal carbon atoms, the molar amount ofsaid polyester and said free glycol combined being essentiallyequivalent to the molar amount of said diphenyl diisocyanate wherebythere are essentially no unreacted isocyanate or hydroxyl groups in thereaction product. Polyesterurethane materials of this type are availablefrom the BF. Goodrich Chemical Company as Estane 5701 and 5707. They arein the form of granules and can be converted into film by milling andcalendering or extruding or by deposition from a solvent cement. Filmsare extremely tough and resistant to scuffing, abrasion and cracking. Inthe recipes of the invention the polyurethane is present in an amount of50 80 parts by weight per 100 parts polyvinyl chloride.

A wide variety of materials such as organic phosphates, low molecularweight polyesters and the like are known as plasticizers for polyvinylchloride. As will be shown later, however, only one plasticizer appearsto be effective in the composition of the invention. It

is di-Z-ethylhexyl azelate, a commercially available material. Theplasticizer is employed in the range of 20 80 parts per 100 partspolyvinyl chloride.

N,N'-dimethylformamide is the preferred solvent for forming the polymercements that are used herein to spread poromeric forming films.Equivalent solvents are N,N'-dimethy1 acetamide and tetrahydrofuran. Theamount of solvent employed is 500 1000 parts by weight per 100 partspolyvinyl chloride. This range of solvent results in cements havingtotal solids of about 18 30 percent.

Generally a wet film thickness of 20 mils is spread in the practice ofthis invention. Cements of 18 21 percent total solids are preferred forthis. These cements are spread at room temperature and are coagulated byimmersion in a water bath at about 50C.

When thicker films 60 to 140 mils and higher in the wet state, aredesired, cements in the total solids range 22 to 30 percent arepreferred. These higher total solids cements are spread at 50 C and arecoagulated in water baths at about 50C.

The films can be formed on the substrate by any accepted coatingtechnique, calendering, brushing, by a doctor knife apparatus, or bydipping.

In summarythe cements of this invention conform to the following recipe:

Material Parts by Weight Polyvinyl chloride Di-Z-ethylhexyl azelate20-80 Linear Polyesterurethane 50-80 Solvent SOD-i000 DETAILEDDESCRIPTION OF THE INVENTION PREPARATION OF POLYESTERURETI-IANE C. for 3hours.

EXAMPLE I Fluorglas Division Hoosick Falls, New York, Code XM 354-7520.The coating does not adhere strongly to this substrate. Polymers arecoagulated from the cements by immersion of the coated substrate in awater bath at 50C; the films are stripped from the substrate andevaulated for Bally flex, MVT, and appearance under Repeat trialsaccording to recipes H, l, J, K and L, using 20, 40, 80 parts of each ofthe respective plasticizers in place of 60 parts shown above, gave filmsthat ranked about the same in flex and MVT regardless of the amount ofplasticizer.

a microscope at 30X magnification. EXAMPLE 3 Materials A B C D E F GPolyvinyl chloride 100 80 100 100 100 Di-2-ethylhexylazelate. Polyesterurethane Dimethyl formamide Bally flex at 35 F., number 100..

of flexes. MVT (g./sq. n1./24 hrs.) 35... Surface appearance Rou Crosssection (cell structure Non-uniform at 30X).

General comment Stifi, brittle, Stifi, brittle, Collapsed,

pa ial porous. nonporous. collapse of cells.

130 925 695 340. Smooth Very smooth Very smooth. Rough.

Very dense, Uniform Uniform Non-uniform.

uniform. Partial collapse, Flexible, porous, Flexible, Flexible,

bleeding of dry (no porous, collapsed plasticizer. bleeding). dry.cells.

Polyvinyl chloride alone (Run A), as expected from prior art, forms afilm that is too stiff to flex in a shoe material, either upper orlining, and which is almost impermeable. Combining some polyurethanewithpolyvinyl chloride, as has been suggested broadly in the art, Run B,gives a film that is porous and has some permeability, but is too stifffor shoe use. It is known to add plasticizer to polyvinylchloride toimprove the flexibility of films thereof as in Run C. This film hascollapsed to a virtually impermeable state and is nonporous. Addition ofa plasticizer to polyurethane polymer, Run D, provides a film that haslow permeability and shows plasticizer bleeding. Run G, a polyurethanefilm with no plasticizer gives a film which collapses to a rough surfaceand has both low permeability and low flex life. Runs E and F, thecompositions of the invention surprisingly show an excellent balance offilm properties. Neither polyvinyl chloride nor polyesterurethane alonegives a film adequate in permeability. These separate materials stillgave films that were inadequate even with plasticizer added. Only themixture of polymers plus a proper amount of plasticizer gives adequatebalance of properties.

EXAMPLE 2 A series of cements similar to Run E of Example 1, butemploying a variety of plasticizer, is made into films and evaluated bythe procedures shown in Example 1.

Run D of Example 1 was repeated using a range of di-2-ethyl hexylazelate.

Material M N (l min. at 50% E., l min. relax) MVT is uniformly at a highlevel, 35F. flex life increases as amount of plasticizer increases.There is a corresponding decrease in permanent set noted as plasticizerincreases.

1 claim: 1. The method of preparing a poromeric film comprising coatinga cement, said cement comprising in parts by weight polyvinylchloride,high molecular weight homopolymer, sp. viscosity 0.44, inherentviscosity 0.95, specific gravity 1.4, particle size 90 percent less than130-200 microns 100 di-Z-ethyl hexyl azelate 20 80 linearpolyesterurethane, essentially linear polyesterurethane havingessentially no unreacted isocyanate or hydroxyl groups Material H I J KL Polyvinyl chloride lolyestcrurcthane 60.

Epoxidized polyester of intermediate 60.

moLwt.

Epoxidized triglycerides, polyglycol ndipnto and soyu oil containinglecithin, xylene, and l,l.l-trlchlorovtlinnc.

Dioctyl phtlilntc 60 Tricresyl phosphate Tri Z-ethyl hexyl trimellitatcDimcthyl formamidc Bally flex at 35 F l0,000 3,200 5, 12,000. MVT 046563 .r. 326 928.

Smooth Slightly rough Slightly rough Slightly rough. Slightly rough.Cross sect1on(30 Fine ine Fine, non-uniform... Non-uniform Non-uniform.General comment Good MVT, poor flex" Good MVT, poor llex P001 film Poorfilm Poor film.

a solvent selected from the group consisting of 2. The method of claim 1wherein said cement com- N,N"dimethYlfYm,amide, prises in parts byweight dimethylacetamide and tetrahydrofuran 500 polyvinyl chloride 1001,000 on to a water permeable substrate at ambient temperatures, passingthe coated substrate into a water bath to coagulate the surface film andextract the solvent and dimemylformamide drying' di-Z-ethylhexyl azelate80 polyesterurethane 6O

2. The method of claim 1 wherein said cement comprises in parts byweight polyvinyl chloride - 100 di-2-ethylhexyl azelate - 80polyesterurethane - 60 dimethylformamide - 900.